Method and device for manufacturing semiconductor or insulator/metallic laminar composite cluster

ABSTRACT

A semiconductor or nonconductor vapor is generated by sputtering targets  11 U,  11 D in a first sputtering chamber  10 , while a metal vapor is generated by sputtering targets  21 U,  21 D in a second sputtering chamber  20 . The semiconductor or nonconductor vapor and the metal vapor are aggregated to clusters during travelling through a cluster-growing tube  32  and injected as a cluster beam to a high-vacuum deposition chamber  30 , so as to deposit composite clusters on a substrate  35 . The produced composite clusters are useful in various fields due to high performance, e.g. high-sensitivity sensors, high-density magnetic recording media, nano-magnetic media for transportation of medicine, catalysts, permselective membranes, optical-magnet sensors and low-loss soft magnetic materials.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of producing compositeclusters, wherein a metal is lamellarily compounded with a semiconductoror nonconductor, useful as various functional elements, and also relatesto an apparatus for production of such composite clusters.

BACKGROUND OF THE INVENTION

Aggregate of fine particles are useful as functional elements, e.g. gassensors and permselective membranes, in various industrial fields due toits big specific surface area and good affinity with an atmospheric gas.

Various methods have been proposed so far for producing aggregate offine particles. For instance, starting material is evaporated andcondensed to fine particles in vapor-phase synthesis. According to acolloidal process, fine particles are precipitated from an electrolyticliquid and stabilized with a surfactant. An aerosol process for sprayingand pyrolysis of a metal ion-containing liquid, a gas-atomizing processfor spraying a mixture of molten metal with an inert gas through anozzle, and a milling process for mechanically crushing solid materialare also proposed for production of such aggregate.

The aerosol process, the milling process and the gas-atomizing processare advantageous for mass-production of clusters but unsuitable forproduction of clusters, which have particle size conditioned tonanometer order for performance originated in nano-sized particles. Thecolloidal process can not avoid inclusion of impurities in a product,although clusters of several nanometers in particle size can bemass-produced. The inclusion of impurities degrades quality of theproduct.

On the other hand, the vapor-phase process promotes growth of clustersin a clean vacuum atmosphere without invasion of impurities. Theclusters produced by the vapor-phase process has a chemically activesurface effective for improvement of functionality. However, the activesurface causes unfavorable oxidation and coalescence of clusters, whenfine particles are deposited on a substrate. The oxidation andcoalescence impede realization of the functionality originated innano-sized particles, regardless of very fine clusters.

SUMMARY OF THE INVENTION

The present invention aims at production of metal/semiconductor ormetal/nonconductor composite clusters, which exhibit various propertiesoriginated in composite structure, under stable conditions, bycompounding metal clusters with semiconductor or nonconductor clustersin a high-vacuum atmosphere.

According to the present invention, a semiconductor or nonconductorvapor is generated by sputtering a semiconductor or nonconductor target,while a metal vapor is generated by sputtering a metal target. Thesesputtering processes are conducted simultaneously but in each systemindependent from the other. A mixture of the metal vapor with thesemiconductor or nonconductor vapor is fed into a cluster-growing tubeand then injected as a cluster beam to a substrate preset in andeposition chamber held at a high degree of vacuum. The mixture isdeposited as composite clusters on the substrate.

The present invention also proposes an apparatus for production ofcomposite clusters. A semiconductor or nonconductor target is preset ina first sputtering chamber. A metal target is preset in a secondsputtering chamber. A movable partition is located between the first andsecond sputtering chambers. The sputtering chambers communicate througha cluster-growing tube with an deposition chamber held at a high degreeof vacuum. The cluster-growing tube is directed to a substrate, which ispreset in the deposition chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional side view illustrating a compositecluster-manufacturing apparatus shown from a side of sputteringchambers.

FIG. 2 is a sectional plan view illustrating the same apparatus.

FIG. 3 is a diagram illustrating some examples of composite clusters,which were produced by the inventive process.

BEST MODES OF THE INVENTION

The present invention uses a composite cluster-manufacturing apparatusschematically shown in FIGS. 1 and 2. The apparatus has a firstsputtering chamber 10 and a second sputtering chamber 20, each separatedfrom the other by a movable partition 31.

A couple of targets 11U and 11D are located in the first sputteringchamber 10. The targets 11U and 11D face to each other with a gap of 10cm or so. Inert gas such as Ar is fed through a supply tube 12 to aspace between the targets 11U and 11D. The targets 11U, 11D aresemiconductive or nonconductive material, in the case where thesputtering chamber 10 is operated for generation of a semiconductor ornonconductor vapor. When a high voltage is applied between the targets11U and 11D from a high-frequency power source 13, glow discharge occursbetween the targets 11U and 11D, and the targets 11U, 11D are sputteredby ionized inert gas atoms, resulting in vaporization of thesemiconductive or nonconductive material. The targets 11U and 11D may bepartially covered with shields 14U and 14D, so as to limit aglow-discharging area.

The second sputtering chamber 20 also has a couple of targets 21U and21D and a supply tube 22 for introduction of inert gas to a spacebetween the targets 21U and 21D. The targets 21U, 21D are conductivematerial, e.g. a transition metal, in the case where the sputteringchamber 20 is operated for generation of a reactive metal vapor. When ahigh voltage is applied between the targets 21U and 21D from a D.C.power source 23, glow discharge occurs between the targets 21U and 21D,and the targets 21U, 21D are sputtered by ionized inert gas atoms,resulting in vaporization of the conductive material. The targets 21Uand 21D may be partially covered with shields 24U and 24D, so as tolimit a glow-discharging area.

Generation of the semiconductor or nonconductor vapor is performed underdifferent conditions from generation of the metal vapor. For instance,gaps between the targets 11U and 11D and between the targets 21U and 21Dare adjusted to approximately 10 cm, while gaps between the targets 11U,11D and the shields 14U, 14D and between the targets 21U, 21D and theshields 24U, 24D are adjusted to approximately 0.2 mm so as to inhibitarc-discharge therebetween. Internal pressures of the sputteringchambers 10, 20 are held at a relatively higher value, e.g. 133-1333 Paby introduction of Ar gas. Glow-discharge necessary for vaporization ofthe targets 11U, 11D and 21U, 21D is started by application ofpredetermined voltages between the targets 11U and 11D and between thetargets 21U and 21D.

When sputtering conditions, e.g. currents and voltages, for the targets11U, 11D and 21U, 21D are independently controlled, interference betweenthe targets 11U, 11D and 21U, 21D is avoided. Compositions of the metalvapor and the semiconductor or nonconductor vapor as a cluster sourceare properly adjusted by control of electric powers applied to thetargets 11U, 11D and 21U, 21D.

The semiconductor or nonconductor vapor and the metal vapor are carriedas a mixture V by an inert gas stream from the sputtering chambers 10,20 through a cluster-growing tube 32 and a nozzle 33 to a depositionchamber 30. The deposition chamber 30 is preferably held at a degree ofvacuum less than a few Pa, in order to assure a smooth flow of thegaseous mixture through the cluster-growing tube 32. The high-vacuumdeposition chamber 30 is also advantageous for suppressing coalescenceof clusters, which have flown into the deposition chamber 30.

A flow rate of the gaseous mixture V, which is carried to thecluster-growing tube 32, and a flow ratio of the semiconductor ornonconductor vapor to the metal vapor are controlled by sputteringconditions in the sputtering chambers 10, 20 and positioning of themovable partition 31. Nano-sized lamellar clusters, i.e. compositeclusters of the metal with the semiconductor or nonconductor is formedand grown up to nanometer size, during travel of the gaseous mixture Vthrough the cluster-growing tube 32,

The composite clusters are passed through the cluster-growing tube 32and injected together with an Ar gas stream from the nozzle 33 bydifferential, since the deposition chamber 30 is evacuated by amechanical booster pump 34. The nozzle 33 is directed to the substrate35 in the deposition chamber 30, and a distance from the nozzle 33 tothe substrate 35 is variable by adjustment of a handling shaft 36. Athickness sensor 37, e.g. a crystal oscillator, is provided between thenozzle 33 and the substrate 35, in order to measure a deposition rate ofthe clusters on the substrate 35 and an effective thickness of adeposition layer. A position of the thickness sensor 37 in relation withthe substrate 35 is controllable by adjustment of a movable shaft 38.

Atoms and molecules vaporized from the targets 11U, 11D and 21U, 21D arefed together with Ar as a carrier gas into the cluster-growing tube 32.The atoms, the molecules and the Ar atoms repeatedly come into ternarycollision and forms cluster nuclei in the tube 32 while discharging alatent heat. The cluster nuclei are gradually grown up to compositeclusters while absorbing gaseous atoms. Since the clusters are formed ina material stream from the sputtering chambers 10, 20 to the depositionchamber 30, growth of the clusters depends on a flow rate of thematerial stream.

A growth mode of clusters in a plasma-gas condensation process isexplained by (1) mutual collision and coalescence of clusters and (2)successive deposition of a metal vapor on embryos as cluster nuclei.Probably, deposition and re-vaporization of metal atoms on and from thecluster nuclei are repeated at an early stage, and clusters come intomutual collision and coalesce together at a latter stage. Since sizedistribution of the clusters as a whole is determined by these actions,production of mono-disperse clusters is expected by introducing clustersto a high-vacuum atmosphere and depositing them on a substrate beforecoalescence.

The cluster-growing tube 32 enables mixing the semiconductor ornonconductor clusters with the metal clusters in a high-vacuumatmosphere, so as to produce the composite clusters that thesemiconductor or nonconductor clusters are compounded with the metalclusters in various state. For instance, when the semiconductor ornonconductor clusters, which are deposited on the metal clusters as acore, form shelly surface layers, further coalescence of metal clusterson the substrate is inhibited, so that properties originated innano-size are imparted to the metal clusters.

Multi-layered composite clusters, which have metal clusters as a core,are bestowed with predetermined properties by controlling number of thesemiconductor or nonconductor clusters coalescent to the metal clustersin correspondence to a relative size of the semiconductor ornonconductor clusters with the metal clusters or by depositing thesemiconductor or nonconductor clusters as several layers, as shown inFIG. 3. Moreover, coalescence and mixing of the semiconductor ornonconductor clusters with the metal clusters are limited in a zoneinside the cluster-growing tube 32 by insertion of the partition 31. Thecoalescence and mixing can be started at an earlier stage by detachmentof the partition 31 on the contrary. Size-control of the semiconductoror nonconductor clusters as well as the metal clusters is performed bychanging electric powers applied to the targets 11U, 11D and 21U, 21D, apressure and a temperature of an inert gas and/or a length of thecluster-growing tube 32. A shape of the multi-layered composite clustersis variously varied in response to the size-control, as shown in FIG. 3.

The other features of the present invention will be apparentlyunderstood from the following examples.

A first sputtering chamber 10 was held at an internal pressure of 500 Paby introduction of Ar as an inert gas at a flow rate of 150 sccm. Sitargets. 11U, 11D, which were preset in the chamber 10, were sputteredat an electric power of 100 W for generation of Si vapor. Fe targets21U, 21D, which were preset in a second sputtering chamber 20 held at aninternal pressure of 500 Pa by introduction of Ar at a flow rate of 150sccm, were sputtered at an electric power of 400 W for generation of Fevapor.

A glass plate as a substrate 35 and a carbon film for TEM observationwere preset in a deposition chamber 30. A nozzle 33 of 5 mm in diameterwas attached to a top of a cluster-growing tube 32 and located at aposition faced to the substrate 35. A distance between the nozzle 33 andthe substrate 35 was adjusted to 5 cm. The chamber 30 was held at 1×10⁻⁴Pa as an initial pressure and 300K.

A gaseous mixture of Si and Fe, i.e. sputtering products, is sucked intothe cluster-growing tube 32 by a differential pressure between thesputtering chambers 10, 20 and the deposition chamber 30. When Ar gaspassed through the tube 32 at a flow rate of 300 sccm and velocity of0.5 m/sec., an internal pressure of the deposition chamber 30 reached 1Pa. Collision and coalescence of Si and Fe atoms were repeated, whilethe gaseous mixture was travelling through the cluster-growing tube 32.The resultant mixture was injected as a cluster beam through the nozzle33 to the substrate 35 at a velocity of 300 m/sec. Consequently, Si andFe clusters were deposited on the substrate 35 at a rate of 1 nm/sec.

A position of the partition 31 was changed under the above conditions,in order to investigate positional effects of the partition 31 on astructure of composite clusters.

Under the condition that a zone for coalescing and mixing thesemiconductor clusters with the metal clusters was limited to an innerspace of the cluster-growing tube 32 by insertion of the partition 31,Si clusters, which have grew to 5 nm in diameter, were mixed with Feclusters. As a result, composite clusters had particle size of 10 nm inaverage with distribution of 8-12 nm and the structure (a) in FIG. 3that a few Si clusters of 5 nm or less in diameter coalesced to Feclusters.

A zone for coalescing and mixing the semiconductor clusters with themetal clusters is widely expanded by detachment of the partition 31.When the targets 11U, 11D and 21U, 21D were sputtered with 100 W and 400W, respectively, without insertion of the partition 31, Si clusters of 1nm in diameter were mixed with Fe clusters of 10 nm in diameter at anearlier stage. Since Si clusters had a bigger surface energy than Feclusters due to the differential particle size, Fe clusters were coatedwith Si clusters. Consequently, the produced composite clusters had thestructure (d) in FIG. 3 that many Si clusters were multi-layered on Feclusters.

In correspondence to change of an effective area of the partition 31 to⅔ and ⅓, the structures of composite clusters were changed to (b) and(c) in FIG. 3, respectively.

The positional effects of the partition 31 on coalescence of Siclusters, as the above, enables production of composite clusters withvarious structures. Since properties of the composite clusters isdifferentiated by the structure, the composite clusters suitable for acertain purpose can be offered by control of the structure. Forinstance, the composite clusters (a), which have relatively big Siclusters coalesced to Fe clusters, are super paramagnetic as anaggregate of single-domain Fe particles at a normal temperature. Theother composite clusters (b)-(d), which have relatively small Siclusters coalesced to Fe clusters, are ferromagnetic at a normaltemperature due to dipole-dipole interaction between the particles.Coercivity of the composite clusters (b) was 800 A/dm, and coercivity ofthe composite clusters (d) was 80 A/dm. That is, coercivity is reducedas a decrease of Si cluster layers in total thickness on Fe clusters,but any of the composite clusters (b)-(d) is useful as functionalmaterial with low-loss soft magnetic property.

INDUSTRIAL APPLICABILITY OF THE INVENTION

According to the present invention as mentioned above, a semiconductoror nonconductor vapor and a metal vapor are generated in sputteringchambers, each of which is independently operated from the other, andcarried as a gaseous mixture through a cluster-growing tube to ahigh-vacuum deposition chamber. Composite clusters, which are formed andgrown up in the cluster-growing tube, are deposited on a substrate,which is preset in the deposition chamber, without repetition ofcoalescence and aggregation, so that mono-disperse composite clusters ofa semiconductor or nonconductor compounded with a metal can be produced.Since a compounded structure of the clusters is changed by controlling aposition of a movable partition between the sputtering chambers and/orflow rates of Ar, the metal vapor and the semiconductor or nonconductorvapor, various properties are imparted to the composite clusters. Theproduced composite clusters are useful in various fields due to highperformance, e.g. high-sensitivity sensors, high-density magneticrecording media, nano-magnetic media for transportation of medicine,catalysts, permselective membranes, optical-magnet sensors and low-losssoft magnetic materials.

1-2. (canceled)
 3. A method of producing composite clusters of asemiconductor or nonconductor with a metal, comprising: sputtering atleast one semiconductor or nonconductor target to generate asemiconductor or nonconductor vapor in a first sputtering chamber;simultaneously sputtering at least one metal target to generate a metalvapor in a second sputtering chamber independently operated from thefirst sputtering chamber; carrying both the semiconductor ornonconductor vapor and the metal vapor as a gaseous mixture into acluster growing tube, wherein composite clusters are formed from thegaseous mixture; and injecting a cluster beam through a nozzle of thecluster-growing tube to a substrate preset in a high vacuum depositionchamber, so as to deposit composite clusters on the substrate.
 4. Themethod of claim 3, wherein a movable partition is located between thefirst and second sputtering chambers which, when the moveable partitionis moved, the change in position of the moveable partition affects theformation of the composite clusters, enabling formation of compositeclusters with various structures.
 5. The method of claim 3, whereininternal pressures of the sputtering chambers are held at a relativelyhigher value than the deposition chamber by evacuating air from thedeposition chamber with a mechanical booster pump in order to assure asmooth flow of the gaseous mixture through the cluster-growing tube. 6.The method of claim 3, wherein the distance between the nozzle and thesubstrate is varied by adjusting a handling shaft attached to thesubstrate.
 7. The method of claim 3, wherein a thickness sensorcontrolled by adjusting a movable shaft attached thereto is providedbetween the nozzle and the substrate in order to measure a depositionrate of the cluster beam on the substrate and an effective thickness ofa deposition layer.
 8. The method of claim 3, wherein the firstsputtering chamber and the second sputtering chamber each has a supplytube therein for introducing an inert gas to a space between thetargets.
 9. The method of claim 3, wherein the at least onesemiconductor or nonconductor target and the at least one metal targetis partially covered with a shield to limit a glow-discharging area. 10.An apparatus for producing composite clusters of a semiconductor ornonconductor with a metal, comprising: a first sputtering chamber,wherein at least one semiconductor or nonconductor target is preset forgeneration of a semiconductor or nonconductor vapor; a second sputteringchamber, wherein at least one metal target is preset for generation of ametal vapor, said first sputtering chamber and said second sputteringchamber communicating through a cluster-growing tube; a movablepartition located between the first and second sputtering chambers; ahigh-vacuum deposition chamber communicating with the cluster-growingtube; and a nozzle attached to a top of the cluster-growing tube anddirected to a substrate preset in the high-vacuum deposition chamber,wherein the semiconductor or nonconductor vapor and the metal vapor areinjected as a cluster beam to the substrate.
 11. The apparatus of claim10, wherein the movable partition is located between the first andsecond sputtering chambers which, when the moveable partition is moved,the change in position of the moveable partition affects the formationof the composite clusters, enabling formation of composite clusters withvarious structures.
 12. The apparatus of claim 10, wherein internalpressures of the sputtering chambers are held at a relatively highervalue than the deposition chamber by evacuating air from the depositionchamber with a mechanical booster pump in order to assure a smooth flowof the semiconductor or nonconductor and metal vapors through thecluster-growing tube.
 13. The apparatus of claim 10, wherein thedistance between the nozzle and the substrate is varied by adjusting ahandling shaft attached to the substrate.
 14. The apparatus of claim 10,wherein a thickness sensor controlled by adjusting a movable shaftattached thereto is provided between the nozzle and the substrate inorder to measure a deposition rate of the cluster beam on the substrateand an effective thickness of a deposition layer.
 15. The apparatus ofclaim 10, wherein the first sputtering chamber contains twosemiconductor or nonconductor targets facing each other with a gaptherebetween and the second sputtering chamber contains two metaltargets facing each other with a gap therebetween, each semiconductor ornonconductor target and metal target partially covered with a shield tolimit a glow-discharging area.
 16. The apparatus of claim 15, whereinthe first sputtering chamber and the second sputtering chamber each hasa supply tube therein for introducing an inert gas to a space betweenthe targets.
 17. An apparatus for producing composite clusters of asemiconductor or nonconductor with a metal, comprising: a firstsputtering chamber, wherein at least one semiconductor or nonconductortarget is preset for generation of a semiconductor or nonconductorvapor; a second sputtering chamber, wherein at least one metal target ispreset for generation of a metal vapor, and wherein each sputteringchamber has a supply tube therein for introducing an inert gas to the atleast one target, and further wherein said first sputtering chamber andsaid second sputtering chamber communicate through a cluster-growingtube; a shield that partially covers each target to limit aglow-discharging area. a movable partition located between the first andsecond sputtering chambers, wherein when the moveable partition ismoved, the change in position of the moveable partition affects theformation of the composite clusters, enabling formation of compositeclusters with various structures; a high-vacuum deposition chambercommunicating with the cluster-growing tube, wherein internal pressuresof the sputtering chambers are held at a relatively higher value thanthe deposition chamber by evacuating air from the deposition chamberwith a mechanical booster pump in order to assure a smooth flow of thesemiconductor or nonconductor and metal vapors through thecluster-growing tube; a nozzle attached to a top of the cluster-growingtube and directed to a substrate preset in the high-vacuum depositionchamber, wherein the semiconductor or nonconductor vapor and the metalvapor are injected as a cluster beam to the substrate, and furtherwherein the nozzle and the substrate is varied by adjusting a handlingshaft attached to the substrate; and a thickness sensor controlled byadjusting a movable shaft attached thereto between the nozzle and thesubstrate in order to measure a deposition rate of the cluster beam onthe substrate and an effective thickness of a deposition layer.